In recent years, automated analytical instruments offering a variety of analytical methods have become commercially available. Modern analytical instruments usually are adapted to process samples contained in standard sample vessels such as test tubes. In order to process many samples in a batch-wise or continuous manner, it is known to arrange plural test tubes in dedicated tube holders usually referred to as “tube racks”. In order to identify samples and allocate test results to specific samples, it is convenient to attach labels to the test tubes providing machine-readable information with respect to the samples contained.
Modern analytical instruments usually come with stationary readers for reading the information provided by the labels of test tubes. Consequently, the labels of the test tubes are to be brought in an appropriate reading position with respect to the reader so that the information can be retrieved. However, due to the fact that test tubes usually are held in a loose-fit manner in the tube rack, the test tubes may be subject to inadvertent rotational movements, especially when the tube rack is handled, e.g., for transport purposes, so that the angular position of the test tubes may be undefined. Accordingly, when it comes to reading of the sample information, the labels may not be readable so that the information cannot be retrieved. It, therefore, may be required to rotate the test tubes to make the labels readable.
It is known to use test tube grippers for the automated rotation of test tubes. Grippers, however, are rather cost-expensive and require much constructional space which is detrimental to the down-sizing of instruments. Furthermore, grippers are complicated in construction and require a highly sophisticated control to achieve sufficient process safety. Moreover, the use of grippers may cause an increased wear of the test tubes.
U.S. Pat. No. 6,081,326 discloses a device, capable of coming laterally in contact with a test tube contained in a tube rack, for rotating the test tube by friction.